Well, a wise person once told me that arguing with the internet is a waste of my time, so your comments I'll leave alone. I came here asking a question that we are still trying to sort out an answer to. How I decide to use the information is entirely my business. Volvo's and wagons and me are inextricably forever linked, so this is the canvas I chose to doodle on.

There is currently someone on ebay that has a set of the wheels in question claiming to be a genuine set, but failed to comment when I asked for additional pictures of the wheel and for a weight request. Maybe someone else could have better luck get more participation out of the seller?

https://www.ebay.com/itm/AUTHENTIC-J...8/321697099475

But yes, it is very possible that the "light weight forged" claim in the factory XK R-S brochure is a misnomer, and in reality it's just a "high strength with nominal weight savings" or something of the kind. If that's the truth, it is what it is. There seems to be a lot of production cars offering forged wheels as part of the premium wheel offerings on cars in the <$100k range, but I wonder how much lighter those are? If they are only stronger, stronger is still better, especially as we move to larger and larger wheels with less and less tire. Seems there are far more Forged mono block designs being offered compared to the multi piece wheels that was common to see the "premium wheel catalogs." The XK X100 had a good half dozen multi piece wheel options for that production run, but the x150 had only two or three?

Forged > multi piece > cast? It's mostly aesthetics at the end of the day really, but it's interesting.

 

That is the point I tried to make earlier from the quote from JLR about their new Range Rover or whatever it was. They made a big deal about 21" forged wheel being about the same weight as the 20" cast one. The weight difference is really not that great - not always anyway. So a not very light forged wheel may well really be forged.

 

My point is, its disingenuous not to worry about the weight of a luggage rack on a Wagon before worrying about the wheels.

He would have been better off attaching helium balloons to the luggage rack.

 

It probably does not make much difference on big, heavy road cars, but weight saved at the wheels, brakes, tyres does reduce unsprung weight, which should help the suspension do better what it is supposed to - keep the tyres pressed to the road. However, 1 kg either way, when the wheel, tyre and brake disc on a 5.0 S/C Jaguar alone weigh in at about 40- 45kg, is not going to be noticable.

 

Winston Churchill once said,
a man trying to save weight on a Volvo wagon, is like a man standing in a bucket trying to lift himself up.

 

I'd appreciate it if we focused on the question and avoided commenting on the car choice. Folks' choice of cars tends to be personal, and Jaguar owners in particular should be sensitive to this given we mostly all dance to a different drummer which is why we drive Jaguars... And saving on unsprung weight is a valid concern. (As a side note I think the Volvo looks really nice with the Jaguar wheels though I'd likely find a way to replace the center caps with Volvo logos myself).

 

Rotational mass is even more important than the unsprung weight.

The wheel has to be spun and not just carried.

 

This only holds true in drag racing, where road conditions are perfectly smooth and unchanging.
Otherwise unsprung weight will always have the final say in how well your tires grip in the real world. How quickly you can rotate is meaningless when it is not in contact with the road.

V

 

No, it also makes a noticeable different in braking requirements.

Less work for the brakes when on a mountain road or a track is a good thing.

The total work required to bring the wheel to velocity of 25MPH from 75MPH is not the same as to bring a similar unsprung mass that isn't connected to t he road from 25MPH to 75MPH.

It will also effect gyroscopic forces as well, although this is more subtle.

I should have chosen rotational inertia instead of rotational mass.

I was also referencing that two wheels of the same weight can yield different performance.

Wheel weight is not the only consideration.

 

Exactly, it should be the lowest priority.
Because for many reasons you are going to have heavy wheels and brakes. Its an immovable object. Especially on a 6 passenger car where wheel strength, and tire load, is paramount.
What is changeable without limitation is power, which easily overcomes whatever weight you want to add to the wheels.
Sure handling will be compromised, but that bridge was crossed when we exceed 1 occupant.

 

I do think we are close in understanding, but from my experience, inertia does not alter the fact that no wheel works at all, if it is not in contact with the asphalt. Rotational inertia is most certainly real, but can be dealt with utilizing a proper braking system. Though higher torque would be needed, the minor inertia differences would never exceed a proper brakes ability to achieve complete wheel lockup within milliseconds of each other.

The total mass of the unsprung weight on the other hand makes or breaks the amount of time your tread has effective contact with the surface. When unsprung weight goes down, all aspects of the car are improved. Braking, acceleration, cornering and comfort all rely on a tire being in a position to utilize its own strengths.

That said, stating ' Rotational mass is even more important than the unsprung weight' is not an accurate statement in my opinion.

'Where the rubber meets the road' is more than a general saying...

 

Think of the Lotus 88.

A lot of unsprung mass, yet keeping the tires planted.

 

The pic you show is of a counterfeit wheel. I have a real XKR-S and Vulcan alloys carry proper Jag part numbers stamped on the rear of the spokes plus they're $1000 EACH (if you can find any, which you probably won't) as Jag only made 200 cars.

 

Since posting this I've been hanging out more in circles where forged wheels show up more commonly and I think they were genuine, or at least, the numbers not being stamped on the spokes like a normal wheel is actually an indication that they were forged vs cast. I have a set of forged Audi wheels hanging out with me right now and they look the same on the back with the part numbers and logos pinged into the wheel.

Doing a searches for other manufacturers with factory forged wheels (VAG has quite a few sets) or even high quality aftermarket (like BBS and HRE), the markings are the same or they have an actual printed adhesive sticker attached to the wheel for part numbers or details. Very very few forged wheels have the numbers embossed on the wheel like is always seen in a cast wheel. I did see a close to new Bentley wheel that had them embossed, but maybe the machining processes are getting better and they can now do it?

Every older forged wheel I've looked has flat spokes on the back.

So, what are your wheels? I would love to get some weights to see where that comes out at. The 19" Audi wheels I currently have I was clued into them being forged because they were lighter to lug them around.

So.... I've found some answers but some mysteries continue to be unanswered.

FYI: a dealer close to me also got in a 2012 XK R-S with this same set of wheels and I naturally inspected it and it also had non-embossed stamping on the wheels. So.... What wheels do you have? Is there forged and non-forged versions of the same wheel? Or maybe it was sent to a different company was contracted to create them which answers the stamping question? The F-Type forged wheels are stamped the same as my original set, so we have to assume JLR continued the same manufacture until very recently.

 

Think about this:

Cast wheels are made by molten material being poured into a mold cavity and the ID letters, numbers are cavities within the cavity that fill with material when cast.

A forged wheel is manufactured from a billet, or a large square piece of solid metal. The billet is heated to extreme temperatures and pressurized to take its shape. This thermal cycle process causes forged wheels to be stronger than cast wheels due to grain refinement. Wheels made this way have numeric/alpha ID engraved into them or stamped into them, the ID would not be raised .... just sayin ... don't think you have phony wheels, nearly certain they are genuine.